Certain solutions, e.g. containing sugar, possess the property of being able to rotate the plane of linear polarized light. The degree of rotation of the plane of vibration per unit of the solution traversed by the polarized light varies in accordance with the concentration of the solution. It is well known in the art to use a device having a light polarizer and an analyzer to measure the rotation of the plane of vibration of light passing through a solution, and to thereby determine the percent sugar content of the solution. One example of such an apparatus is shown in U.S. Pat. No. 3,411,342. In this patent, the polarimeter consists of a mercury vapor lamp light source, a collimating lens, a primary polarizer to establish a reference point for measurement of optical rotation, a sample cell through which a continuous stream of crude syrup is circulated, and a measuring circuit that determines the extent of optical rotation caused by the sample and provides an appropriate output signal.
Such conventional polarimeters of the prior art generally use visible light sources in the 400-700 nanometer wavelength emission range.
U.S. Pat. No. 4,467,204 describes a polarimeter system and method using an infrared light source to gauge and measure the optical rotation of dark sugar solutions.
German Patent No. 2724543 and U.S. Pat. Nos. 3,724,957; 4,699,514 and 4,671,660 disclose multi-beam measurement of polarimetry.
U.S. Pat. No. 5,009,230 describes a device for polarimetrically measuring the concentration of blood glucose by producing two alternating linearly polarized states of infrared light, passing these through a sample, detecting the intensities of these two states after passing through the sample and detector and calculation means for measuring the ratio of the sum and differences of the transmitted intensities.
U.S. Pat. Nos. 4,167,676; 4,350,163; 4,427,889; 4,586,513 and 4,655,225 describe polarimetric devices using absorption and/or backscattering of incident radiation to determine glucose levels.
None of these known devices have the sensitivity achievable by more rigorous available analytical techniques. The degree of rotation caused by glucose levels of the body, for example, is very small and is normally difficult to measure with any sensitivity without using large and bulky equipment and invasive procedures.